1. Technical Field
The present invention relates to an imaging system and devices for medical, automotive, photographic and other applications.
2. Related Background Art
Wide-angle lenses are useful for a variety of applications including medical application such as endoscopes, security cameras, automotive cameras and imaging systems for photography. As the field of view increases, geometric lens distortion becomes un-avoidable. The straight lines at the off-axis field points become curved. Distortion can be minimized with appropriate lens design. Lenses are also designed with particular geometric distortion properties to match the application. Lenses may be designed to provide the best overall visual appearance and the ability to detect details in particular regions of the image. Such lenses, termed here as, Tailored Distortion Lenses, reduce distortion optically by using a combination of spheric and aspheric elements. However, sometimes significant amount of distortion can still be easily seen even in a tailored distortion lens. To further reduce the distortion of a tailored distortion lens through the design of the optics is very difficult and may require undesirable compromises of other lens parameters. However the remaining distortion can be further reduced or optimized for particular applications or particular situations in an application by processing the image data. The processed image is then displayed to the user or saved to a memory for further processing. The resulting image will have less distortion than what can be accomplished optically alone. For certain applications, the resulting images provide better views of important features, are most pleasing to view and appear more natural to the users.
Zooming is a common feature in many imaging systems. There are two ways to accomplish zooming: optical or digital. In an optical zoom, the components (lens elements, spacers, etc) are moved physically to cause a change in the overall focal length of the system. For example, a typical consumer camera employs an optical zoom lens having moving lens groups. For a given image size (film or the imaging sensor), this means that the overall field of view of the system is also changing during zooming. The field of view is reduced for increased focal length and vice versa. Digital zooming is a process in which a smaller section of an image is enlarged to fill the entire available area of the display. When a smaller section is enlarged, one loses field of view because image areas outside the zoomed area can no longer be displayed. There is a need to zoom in on an area of interest, yet simultaneously be able to see the full field of view.
Corrections of the geometric distortion heretofore required algorithms specific to each lens design. There is a need for an algorithm that accurately and generally describes lens behavior. With such a function there would be a reduced need to design a custom lens for each application. Similarly, heretofore color and geometric corrections have been accomplished in software through empirical measurements and numeric approximation of the lens mapping. Often the lens mapping function is described as a polynomial expansion containing multiple empirically determined terms specific to the particular lens. Measurements for calculating the particular algorithms require use of data from broad areas of the lens. In other cases a linear approximation for lens behavior is used that is good for only a narrow section of the image. There is a need for a descriptive function of lens behavior that applies to multiple lens designs, is applicable to the entire viewing region of the lens and can be calculated using data from a narrow region of the lens. This makes the embedding of processing algorithms easier for certain types of electronic imagers.
The image from a single lens can be modified to simulate the behavior of a different lens. Applications such as endoscopy require particular lens designs for particular procedures or even for portions of procedures. In some cases there is a need to retract a probe and change the lens or exchange the probe for another with a different lens for a different stage of the procedure. This adds to the complexity of procedures and increases the chance for contamination and infection. Complex mechanical lens elements have been used to enable a modification of the field or direction of view to help enable a single probe to be used throughout a procedure or for multiple procedures. The tradeoff is most often a smaller field of view for the ability to image a limited area. These more complex probes can often lead to a surgeon missing particular features as the field of view is narrowed or the field of view is limited to a particular direction. There is a need for endoscopic probes that can smoothly change the field of view or can smoothly change the image from one lens design to another without the need to physically change the probe.
Wide-angle lenses are also finding increasing use in automotive applications. Imaging systems incorporating wide-angle lenses are used for viewing the region behind a vehicle to eliminate blind spots unavoidable with mirrors or simply the view out the rear window. Geometric distortions in such images may result in effectively blind spots similar to those that the systems are intended to eliminate. The most effective image for driver viewing also varies by the driving situation, the particular drivers, and even driver preferences. There is a need to be able to transform the image of an automotive camera after the camera has been installed in the vehicle. There is additionally a need to be able for the driver to easily transform the image to match a changing driving situation.
There is a need for the ability to process the images captured by an electronic imager to provide modifications of the geometric distortions to the viewed image. There is a need for an image processing method, which accurately describes lens behavior and uses only a minimum number of parameters to characterize the lens mapping function. There is a need for an imaging system that uses lens designs that are tailored to the processing algorithms used to subsequently manipulate the image.
Attempts to provide algorithms have been reported in, for example, U.S. Pat. Re. 36,207, U.S. Pat. No. 7,427,263, U.S. Pat. No. 7,042,508 and U.S. Pat. No. 7,042,497. None of these attempts address the needs discussed above.